Imaging lens and imaging apparatus

ABSTRACT

An imaging lens consists of, disposed in order from the object side, a front group, a stop, and a rear group, wherein
         the front group includes, in order from the most-object side, a positive first lens, a negative second lens, and a negative third lens which are adjacently disposed,   the rear group consists of two sets of cemented lenses having positive refractive powers and a positive single lens,   the object-side cemented lens is formed by cementing, in order form the object side, a positive lens with a convex surface toward the image side and a negative meniscus lens together,   the image-side cemented lens is formed by cementing, in order from the object side, a negative meniscus lens with a concave surface toward the image side and a positive lens together, and   the image-side cemented lens is disposed at the most-image side of the rear group.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2014-189787, filed in Sep. 18, 2014. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an imaging lens suitable for electroniccameras such as surveillance cameras, industrial cameras, single-lensreflex cameras, non-reflex type cameras, and the like as well as to animaging apparatus equipped with this imaging lens.

Description of the Related Art

The number of pixels of image sensors is increasing in electroniccameras such as surveillance cameras, industrial cameras, single-lensreflex cameras, non-reflex type cameras, and the like, and there isdemand for imaging lenses that favorably correct various aberrationsaccompanying these developments. In addition, there is also demand forimaging lenses that favorably correct small F numbers for the purpose ofphotographing in dark places and compositional intent, such asdefocusing the background.

As imaging lenses to be used in electronic cameras as described above,imaging lenses of a two-group configuration including a front group anda rear group are known. Patent Documents 1 and 2 (Japanese UnexaminedPatent Publication No. 61(1986)-188512 and Japanese Unexamined PatentPublication No. 2013-080151) disclose imaging lenses having such aconfiguration.

SUMMARY OF THE INVENTION

None of the imaging lenses of Patent Documents 1 and 2 have sufficientlysmall F numbers and correct various aberrations adequately. Therefore,there is demand for further high-performance imaging lenses.

The present invention has been developed in view of the foregoingcircumstances. The object of the present invention is to provide animaging lens that corrects various aberrations favorably having a smallF number, and to provide an imaging apparatus equipped with this imaginglens.

An imaging lens of the present invention consisting of, in order fromthe object side, a front group, a stop, and a rear group, wherein

the front group includes, in order from the most-object side, a firstlens having a positive refractive power, a second lens having a negativerefractive power, and a third lens having a negative refractive powerwhich are adjacently disposed,

the rear group consists of two sets of cemented lenses having positiverefractive powers and a single lens having a positive refractive power,

the object-side cemented lens of the two sets of cemented lenses isformed by cementing, in order from the object side, a positive lens witha convex surface toward the image side and a negative meniscus lenstogether, and

the image-side cemented lens of the two sets of cemented lenses isformed by cementing, in order from the object side, a negative meniscuslens with a concave surface toward the image side and a positive lenstogether, the image-side cemented lens being disposed at the most-imageside in the rear group.

In the imaging lens of the present invention, it is preferable for thesecond lens to be of a meniscus shape with a concave surface toward theimage side.

It is preferable for the first lens to be of a shape with a convexsurface toward the object side.

Further, it is preferable for the front group to include a final lens,having a positive refractive power, of the front group at the most-imageside.

Further, it is preferable for conditional formulae (1) and (2) below tobe satisfied. Note that it is more preferable for at least one ofconditional formulae (1-1) and (2-1) below to be satisfied:0.05<NnA−NpA<0.8  (1)0.25<NnA−NpA<0.6  (1-1)22<νpA−νnA<70  (2)25<νpA−νnA<65  (2-1)where,NnA: the refractive index of the negative lens of the object-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,NpA: the refractive index of the positive lens of the object-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,νpA: the Abbe's number of the positive lens of the object-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line, andνnA: the Abbe's number of the negative lens of the object-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line.

Further, it is preferable for conditional formulae (3) and (4) below tobe satisfied. Note that it is more preferable for at least one ofconditional formulae (3-1) and (4-1) below to be satisfied:0<NnB−NpB<0.8  (3)0.25<NnB−NpB<0.6  (3-1)22<νpB−νnB<70  (4)25<νpB−νnB<65  (4-1)where,NnB: the refractive index of the negative lens of the image-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,NpB: the refractive index of the positive lens of the image-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d lineνpB: the Abbe's number of the positive lens of the image-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line, andνnB: the Abbe's number of the negative lens of the image-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line.

Further, it is preferable for conditional formula (5) below to besatisfied. Note that it is more preferable for conditional formula (5-1)below to be satisfied:−0.5<f/fF<0.2  (5)−0.45<f/fF<0.1  (5-1)where,f: the focal length of the entire system, andfF: the focal length of the front group.

Further, it is preferable for conditional formula (6) below to besatisfied. Note that it is more preferable for conditional formula (6-1)below to be satisfied:−10<(Rc−Rd)/(Rc+Rd)≦0  (6)−2<(Rc−Rd)/(Rc+Rd)≦0  (6-1)where,Rc: the radius of curvature of the image-side surface of a lens adjacentto the final lens of the front group in the front group, andRd: the radius of curvature of the object-side surface of the final lensof the front group.

Further, it is preferable for conditional formula (7) below to besatisfied. Note that it is more preferable for conditional formula (7-1)below to be satisfied:0.1<fA/fB<10  (7)0.2<fA/fB<8  (7-1)where,fA: the focal length of the object-side cemented lens of the two sets ofcemented lenses in the rear group, andfB: the focal length of the image-side cemented lens of the two sets ofcemented lenses in the rear group.

It is preferable for conditional formula (8) below to be satisfied:−2<f/f123<−0.3  (8),where,f: the focal length of the entire system, andf123: the combined focal length of the first lens through the thirdlens.

Further, the front group may consist of, in order from the object side,the first lens, the second lens, the third lens, a fourth lens having anegative refractive power and the final lens of the front group beingdisposed at the most-image side of the front group. Alternatively, thefront group may consist of, in order from the object side, the firstlens, the second lens, the third lens, a fourth lens being a meniscuslens with a concave surface toward the object side, a fifth lens being anegative meniscus lens with a concave surface toward the image side, anda final lens of the front group being disposed at the most-image side ofthe front group.

Further, the rear group may consist of, in order from the object side,the single lens, the object-side cemented lens, and the image-sidecemented lens. Alternatively, rear group may consist of, in order fromthe object side, the object-side cemented lens, the single lens, and theimage-side cemented lens.

An imaging apparatus of the present invention is equipped with theimaging lens of the present invention described above.

Note that the above expression “consist/consisting of” intends toinclude lenses that practically have no power, optical elements otherthan lenses such as a stop, a mask, a cover glass, a filter, andmechanical components such as lens flanges, a lens barrel, a camerashake correcting mechanism, etc., in addition to those listed above asthe constituent elements.

Further, the surface shapes and the signs of the refractive powers ofthe above lenses should be considered in paraxial regions if asphericalsurfaces are included therein.

An imaging lens of the present invention consists of, in order from theobject side, a front group, a stop, and a rear group, wherein

the front group includes, in order from the most-object side, a firstlens having a positive refractive power, a second lens having a negativerefractive power, and a third lens having a negative refractive powerwhich are adjacently disposed,

the rear group consists of two sets of cemented lenses having positiverefractive powers, and a single lens having a positive refractive power,

the object-side cemented lens of the two sets of cemented lenses isformed by cementing, in order from the object side, a positive lens witha convex surface toward

the image side and a negative meniscus lens together, and the image-sidecemented lens of the two sets of cemented lenses is formed by cementing,in order from the object side, a negative meniscus lens with a concavesurface toward the image side and a positive lens together, theimage-side cemented lens being disposed at the most-image side of therear group. Such a configuration enables an imaging lens that correctsvarious aberrations favorably having a small F number.

Further, an imaging apparatus of the present invention is equipped withthe imaging lens of the present invention. Therefore, bright andhigh-quality images can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens (the same as that of Example 1)according to an embodiment of the present invention.

FIG. 2 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens in Example 2 of the present invention.

FIG. 3 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens in Example 3 of the present invention.

FIG. 4 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens in Example 4 of the present invention.

FIG. 5 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens in Example 5 of the present invention.

FIG. 6 is a cross-sectional diagram that illustrates the lensconfiguration of an imaging lens in Example 6 of the present invention.

FIG. 7 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 1 of the present invention.

FIG. 8 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 2 of the present invention.

FIG. 9 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 3 of the present invention.

FIG. 10 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 4 of the present invention.

FIG. 11 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 5 of the present invention.

FIG. 12 is a collection of diagrams that illustrate aberrations of theimaging lens in Example 6 of the present invention.

FIG. 13 is a perspective view that illustrates the front side of animaging apparatus according to one embodiment of the present invention.

FIG. 14 is a perspective view that illustrates the front side of animaging apparatus according to another embodiment of the presentinvention.

FIG. 15 is a perspective view that illustrates the back side of theimaging apparatus illustrated in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. FIG. 1 is across-sectional view that illustrates the lens configuration of animaging lens according to an embodiment of the present invention. Theexample of the configuration illustrated in FIG. 1 is the same as thatof the imaging lens in Example 1 to be described later. In FIG. 1, theleft side is the object side, and the right side is the image side. Thestop St illustrated in FIG. 1 does not necessarily represent the size orshape thereof, but the positions thereof along the optical axis Z.Further, FIG. 1 represents axial light rays wa and light rays wb havinga maximum angle of view.

As illustrated in FIG. 1, this imaging lens consists of, in order fromthe object side, a front group GF, a stop St, and a rear group GR.

When this imaging lens is applied to imaging apparatuses, it ispreferable for a cover glass, a prism, various types of filters, such asinfrared cut filters and low-pass filters to be provided between theoptical system and the image surface Sim according to the configurationsof a camera on which the lens is mounted. Accordingly, FIG. 1illustrates an example in which a plane parallel optical member PP thatpresumes such components is disposed between the lens system and theimage surface Sim.

The front group GF includes, in order from the most-object side, a firstlens L1 having a positive refractive power, a second lens L2 having anegative refractive power, and a third lens L3 having a negativerefractive power, which are adjacently disposed.

Configuring the first lens L1 to have a positive refractive power insuch a manner is advantageous from the viewpoint of correcting lateralchromatic aberration and shortening the total length. In addition, byconfiguring the second lens L2 to have a negative refractive power, theincident angles of light rays at peripheral angles of view with respectto the rear group GR can be suitably reduced, and the generation ofastigmatism can be reduced. Further, by configuring the third lens L3 tohave a negative refractive power, the incident angles of light rays atperipheral angles of view with respect to the rear group GR can besuitably reduced, and the generation of astigmatism can be reduced aswell.

The rear group GR consists of two sets of cemented lenses havingpositive refractive powers, and a single lens L7 having a positiverefractive power. The object-side cemented lens CA of the two sets ofcemented lenses is formed by cementing, in order from the object side, apositive lens L8 with a convex surface toward the image side and anegative meniscus lens L9 together. The image-side cemented lens CB isformed by cementing, in order from the object side, a negative meniscuslens L10 with a concave surface toward the image side and a positivelens L11 together. This image-side cemented lens CB is disposed at themost-image side in the rear group GR.

By configuring the rear group GR to include two sets of cemented lensesCA and CB having positive refractive powers in such a manner,longitudinal chromatic aberration and lateral chromatic aberration canbe corrected at the cemented surfaces of the cemented lenses. Inaddition, by distributing positive refractive powers among the two setsof cemented lenses CA and CB and a single lens L7, the refractive powerof the entire lens system can be secured while suppressing thegeneration of spherical aberration. Further, by setting the positiverefractive power at the most-image side, the incident angles of chiefrays at peripheral angles of view with respect to the image surface canbe suitably reduced. By configuring the object-side cemented lens CA insuch a manner as described above, spherical aberration and longitudinalchromatic aberration can be corrected while suppressing the generationof astigmatism and the generation of differences in longitudinalchromatic aberration depending angles of view. Further, by configuringthe image-side cemented lens CB in such a manner described above,longitudinal chromatic aberration and lateral chromatic aberration canbe corrected while suppressing the generation of higher order sphericalaberration and the generation of differences in spherical aberrationdepending on wavelengths.

In the imaging lens of the present embodiment, it is preferable for thesecond lens L2 to be of a meniscus shape with a concave surface towardthe image side. Such a configuration enables the generation ofastigmatism to be suppressed while suppressing the fluctuations inastigmatism due to changes in the object distance.

Further, it is preferable for the first lens L1 to be of a shape with aconvex surface toward the object side. Such a configuration enables thegeneration of astigmatism to be suppressed and the total length to beshortened. Note that when the first lens L1 is configured to be ameniscus lens, astigmatism can be corrected more preferably, and lateralchromatic aberration and distortion can be prevented from beingexcessively corrected at large angles of view. This will be advantageousfrom the viewpoint of widening angles of view.

Further, it is preferable for the sixth lens L6 (which corresponds to afinal lens of the front group in the present invention), which isdisposed at the most-image-side in the front group GF, to be a positivelens. Such a configuration enables the incident angles of the axiallight rays with respect to the rear group to be reduced whilesuppressing the generation of spherical aberration.

Further, it is preferable for conditional formulae (1) and (2) below tobe satisfied. By configuring the imaging lens such that the value ofNnA−NpA is not greater than or equal to the upper limit defined byconditional formula (1), spherical aberration can be prevented frombeing excessively corrected. Further, by configuring the imaging lenssuch that the value of NnA−NpA is not less than or equal to the lowerlimit defined by conditional formula (1), spherical aberration can beprevented from being insufficiently corrected. By configuring theimaging lens such that the value of νpA−νnA is not greater than or equalto the upper limit defined by conditional formula (2), longitudinalchromatic aberration can be prevented from being excessively corrected.In addition, by configuring the imaging lens such that the value ofνpA−νnA is not less than or equal to the lower limit defined byconditional formula (2), longitudinal chromatic aberration can beprevented from being insufficiently corrected. Note that more favorablecharacteristics can be obtained by satisfying at least one ofconditional formulae (1-1) and (2-1) below:0.05<NnA−NpA<0.8  (1)0.25<NnA−NpA<0.6  (1-1)22<νpA−νnA<70  (2)25<νpA−νnA<65  (2-1)where,NnA: the refractive index of the negative lens of the object-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,NpA: the refractive index of the positive lens of the object-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,νpA: the Abbe's number of the positive lens of the object-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line, andνnA: the Abbe's number of the negative lens of the object-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line.

Further, it is preferable for conditional formulae (3) and (4) below tobe satisfied. By configuring the imaging lens such that the value ofNnB−NpB is not greater than or equal to the upper limit defined byconditional formula (3), spherical aberration can be prevented frombeing excessively corrected. In addition, by configuring the imaginglens such that the value of NnB−NpB is not less than or equal to thelower limit defined by conditional formula (3), spherical aberration canbe prevented from being insufficiently corrected. By configuring theimaging lens such that the value of νpB−νnB is not greater than or equalto the upper limit defined by conditional formula (4), longitudinalchromatic aberration can be prevented from being excessively corrected.In addition, by configuring the imaging lens such that the value ofνpB−νnB is not less than or equal to the lower limit defined byconditional formula (4), longitudinal chromatic aberration can beprevented from being insufficiently corrected. Note that more favorablecharacteristics can be obtained by satisfying at least one ofconditional formulae (3-1) and (4-1) below:0<NnB−NpB<0.8  (3)0.25<NnB−NpB<0.6  (3-1)22<νpB−νnB<70  (4)25<νpB−νnB<65  (4-1)where,NnB: the refractive index of the negative lens of the image-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,NpB: the refractive index of the positive lens of the image-sidecemented lens of the two sets of cemented lenses in the rear group withrespect to the d line,νpB: the Abbe's number of the positive lens of the image-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line, andνnB: the Abbe's number of the negative lens of the image-side cementedlens of the two sets of cemented lenses in the rear group with respectto the d line.

Further, it is preferable for conditional formula (5) below to besatisfied. By configuring the imaging lens such that the value of f/fFis not greater than or equal to the upper limit defined by conditionalformula (5), a suitable amount of back focus can be maintained. Inaddition, by configuring the imaging lens such that the value of f/fF isnot less than or equal to the lower limit defined by conditional formula(5), an increase in spherical aberration can be prevented, because theamount of the refractive power borne by the rear group GR will notincrease excessively. Note that more favorable characteristics can beobtained by satisfying conditional formula (5-1) below:−0.5<f/fF<0.2  (5)−0.45<f/fF<0.1  (5-1)where,f: the focal length of the entire system, andfF: the focal length of the front group.

Further, it is preferable for conditional formula (6) below to besatisfied. By configuring the imaging lens such that the value of(Rc−Rd)/(Rc+Rd) does not exceed the upper limit defined by conditionalformula (6), spherical aberration can be prevented from beinginsufficiently corrected. In addition, by configuring the imaging lenssuch that the value of (Rc−Rd)/(Rc+Rd) is not less than or equal to thelower limit defined by conditional formula (6), spherical aberration canbe prevented from being excessively corrected. Note that more favorablecharacteristics can be obtained by satisfying conditional formula (6-1)below:−10<(Rc−Rd)/(Rc+Rd)≦0  (6)−2<(Rc−Rd)/(Rc+Rd)≦0  (6-1)where,Rc: the radius of curvature of the image-side surface of a lens adjacentto the final lens of the front group in the front group, andRd: the radius of curvature of the object-side surface of the final lensof the front group.

Further, it is preferable for conditional formula (7) below to besatisfied. By satisfying conditional formula (7), refractive power canbe appropriately distributed, resulting in the generation of sphericalaberration being prevented. In addition, by configuring the imaging lenssuch that the value of fA/fB is not less than or equal to the lowerlimit defined by conditional formula (7), the incident angles of thechief rays at peripheral angles of view with respect to the imagesurface can be suitably suppressed. Note that more favorablecharacteristics can be obtained by satisfying conditional formula (7-1)below:0.1<fA/fB<10  (7)0.2<fA/fB<8  (7-1)where,fA: the focal length of the object-side cemented lens of the two sets ofcemented lenses in the rear group, andfB: the focal length of the image-side cemented lens of the two sets ofcemented lenses in the rear group.

Further, it is preferable for conditional formula (8) below to besatisfied. By configuring the imaging lens such that the value of f/f123is not greater than or equal to the upper limit defined by conditionalformula (8), a suitable amount of back focus can be maintained. Further,the incident angles of light rays at peripheral angles of view withrespect to the rear group GR can be suitably reduced, and the generationof astigmatism can be decreased. Further, by configuring the imaginglens such that the value of f/f123 is not less than or equal to thelower limit defined by conditional formula (8), spherical aberration canbe prevented from becoming worse, and the increase in the total lengthcan be prevented. Note that more favorable characteristics can beobtained by satisfying conditional formula (8-1) below:−2<f/f123<−0.3  (8)−1.5<f/f123<−0.4  (8-1)where,f: the focal length of the entire system, andf123: the combined focal length of the first lens through the thirdlens.

Further, in the imaging lens of the present embodiment, the front groupGF consists of, in order from the object side, a first lens L1, a secondlens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixthlens L6 (a final lens of the front group). Further, the fourth lens L4is a meniscus lens with a concave surface toward the object side, andthe fifth lens L5 is a negative meniscus lens with a concave surfacetoward the image side. By configuring the fourth lens L4, which isdisposed on the object side of the stop St, to be a meniscus lens with aconcave surface toward the object side, pupil aberration will generatebecause a concave surface is on the object side, and a convex surface ison the image side. Further, the position of the entrance pupil will becloser to the object side as angles of view become greater, and theheight, at which light rays at the outermost angles pass themost-object-side surface, will become low. Thereby, the outer diameterof the first lens L1 can be reduced. Further, by configuring the fifthlens L5 to be a negative lens, spherical aberration can be corrected. Inaddition, by configuring the fifth lens L5 to be a negative meniscuslens with a concave surface toward the image side, spherical aberrationand field curvature in the tangential direction can be balanced.

Note that the front group GF may consist of, in order from the objectside, the first lens, the second lens, the third lens, the fourth lens,and the fifth lens (the final lens of the front group). Further, thefourth lens may have a negative refractive power. By configuring thefourth lens to have a negative refractive power in such a manner, theincident angles of the light rays at peripheral angles of view withrespect to the rear group GR can be suitably reduced, and the generationof astigmatism can be decreased.

Further, in the imaging lens of the present embodiment, the rear groupGR consists of, in order form the object side, a single lens L7, theobject-side cemented lens CA, and the image-side cemented lens CB. Byconfiguring the two sets of cemented lenses to be disposed on the imageside in such a manner, lateral chromatic aberration can be easilycorrected.

Note that the rear group GR may consist of, in order from the objectside, the object-side cemented lens, the single lens, and the image-sidecemented lens. By configuring the two sets of cemented lenses to bespaced apart from each other in such a manner, longitudinal chromaticaberration and lateral chromatic aberration can be easily balanced.

Moreover, in the case that the present zoom lens is used in environmentsin which lenses are easily damaged, it is preferable for a multi-layerfilm coating for protection to be applied onto lenses. Moreover, inaddition to a coating for protection, an antireflection coating may beapplied onto lenses so as to reduce ghost light, and the like when usingthe lenses.

Further, FIG. 1 illustrates the example in which an optical member PP isdisposed between a lens system and an image surface Sim. Instead ofdisposing a low-pass filter, various kinds of filters which cut specificwavelength ranges, and the like between the lens system and the imagesurface Sim, these various kinds of filters may be disposed betweenlenses, or a coating, which exhibits the same effects as the variouskinds of filters, may be applied onto the lens surfaces of any of thelenses.

Next, the Examples of numerical values of the imaging lens of thepresent invention will be described.

First, the description will start with an imaging lens of Example 1.FIG. 1 is a cross-sectional view of the lens configuration of theimaging lens of Example 1. Note that the left side is the object sideand the right side is the image side in FIG. 1 and FIGS. 2 through 6which correspond to Examples 2 through 6 to be described later. Further,each of the stop St illustrated in the Figures does not necessarilyrepresent the size or shape thereof, but the position thereof along theoptical axis Z.

In the imaging lens of Example 1, a front group GF consists of sixlenses, and a rear group GR consists of five lenses in which a singlelens L7, the object-side cemented lens CA, and the image-side cementedlens CB are disposed in order from the object side.

Table 1 shows basic lens data of the imaging lens in Example 1, andTable 2 shows data regarding specs. The following will describe themeanings of items represented in the Tables by using Example 1 as anexample. The same basically applies to Examples 2 through 6.

In the lens data in Table 1, the column of the surface numbers shows therespective surface numbers that sequentially increase toward the imageside, with the surface of the constituent element at the most-objectdesignated as first, the column of the radii of curvature shows theradii of curvature of the respective surfaces, and the column of thedistances between surfaces shows the distances between each surface anda surface next thereto along the optical axis Z. In addition, the columnof nd shows the refractive indices of the respective optical elementswith respect to the d line (wavelength: 587.6 nm), and the column of vdshows the Abbe's numbers of the respective optical elements with respectto the d line (wavelength: 587.6 nm).

Here, the signs of the radius of curvature are are positive when asurface shape is convex on the object side, and negative when a surfaceshape is convex on the image side. The basic lens data represents a stopSt and an optical member PP as well. The column of the surface number ofa surface corresponding to the stop St indicates a surface number andthe letters (stop).

The data regarding specs in Table 2 shows focal length f′, back focusBf′, an F number FNo., and a full angle of view 2ω).

In basic lens data and data regarding specs, degrees are used as theunit of angles, and mm is used as the unit of length, but otherappropriate units may also be used, as optical systems are usable evenwhen they are proportionally enlarged or miniaturized.

TABLE 1 DISTANCES SURFACE RADII OF BETWEEN NUMBERS CURVATURE SURFACES ndνd  1 25.33324 2.890 1.51680 64.20  2 53.76621 0.100  3 16.66871 1.0001.71299 53.87  4 7.08951 2.690  5 19.08279 0.820 1.71299 53.87  66.13314 3.470  7 −12.37312 4.100 1.48749 70.24  8 −22.80160 0.150  926.76491 0.820 1.48749 70.24 10 8.86360 1.090 11 24.23688 3.110 1.8340037.16 12 −24.23688 5.590 13(STOP) ∞ 2.140 14 −28.29463 1.960 1.7440044.79 15 −10.43002 0.100 16 54.56991 2.740 1.48749 70.24 17 −7.744001.220 1.84666 23.78 18 −19.35499 0.110 19 11.75932 2.430 1.90366 31.3120 7.51500 3.210 1.49700 81.54 21 −20.81916 6.770 22 ∞ 0.500 1.5163364.14 23 ∞ 0.996

TABLE 2 EXAMPLE 1/SPECS (d line) f′ 4.090 Bf′ 8.096 FNo. 1.85 2ω[°] 98.8

FIG. 7 illustrates aberration diagrams of the imaging lens of Example 1.Note that the diagrams of FIG. 7 respectively illustrate, in order fromthe left, spherical aberration, astigmatism, distortion, and lateralchromatic aberration. Each of the aberration diagrams that illustratespherical aberration, astigmatism, and distortion illustrates aberrationusing the d line (wavelength: 587.6 nm) as a reference wavelength. Thediagram that illustrate spherical aberration show aberrations withrespect to the d line (wavelength: 587.6 nm), the C line (wavelength:656.3 nm), the F line (wavelength: 486.1 nm), and the g line(wavelength: 435.8 nm) which are respectably indicated by a solid line,a long broken line, a short broken line, and a gray solid line. In thediagram that illustrates astigmatism, aberration in the sagittaldirection is indicated by a solid line, and aberration in the tangentialdirection is indicated by a short broken line. In addition, the diagramthat illustrates lateral chromatic aberration shows aberrations withrespect to the C line (wavelength: 656.3 nm), the F line (wavelength:486.1 nm), and the g line (wavelength: 435.8 nm) which are respectablyindicated by a long broken line, a short broken line, and a gray solidline. Note that all of these aberrations are for when the imaging lensis focused at an object at infinity. In addition, “FNo.” in the diagramthat illustrates spherical aberration denotes an F number, and “ω” inthe other aberration diagram denotes a half angle of view.

As the items in the data, the meanings thereof, and the manners in whichthey are shown in the descriptions for Example 1 above apply to theExamples below, redundant descriptions thereof will be omitted unlessotherwise noted.

Next, an imaging lens of Example 2 will be described. The imaging lensof Example 2 has the same configurations of the lens groups as those ofthe imaging lens in Example 1. FIG. 2 is a cross-sectional viewillustrating the lens configuration of the imaging lens of Example 2.Further, regarding the imaging lens of Example 2, Table 3 shows basiclens data, Table 4 shows data regarding specs, and FIG. 8 illustratesthe aberrations.

TABLE 3 EXAMPLE 2/LENS DATA DISTANCES SURFACE RADII OF BETWEEN NUMBERSCURVATURE SURFACES nd νd  1 21.95221 3.260 1.51633 64.14  2 48.443570.100  3 14.66909 1.000 1.71299 53.87  4 6.31383 3.005  5 32.14966 0.8001.71299 53.87  6 5.98668 2.559  7 −17.64405 5.000 1.80000 25.00  8−20.49538 0.100  9 18.73879 1.387 1.80000 26.36 10 8.85934 0.449 1111.36478 4.500 1.79999 29.90 12 −56.36876 3.324 13(STOP) ∞ 2.080 14−42.91383 4.204 1.74734 53.27 15 −12.08141 0.100 16 29.86304 2.7021.61800 63.33 17 −8.45189 0.837 1.90000 25.62 18 −29.05389 0.100 1913.25979 0.810 1.50736 53.64 20 6.37036 3.036 1.49700 81.54 21 −64.289625.000 22 ∞ 0.500 1.51633 64.14 23 ∞ 2.694

TABLE 4 EXAMPLE 2/SPECS (d line) f′ 4.098 Bf′ 8.024 FNo. 1.80 2ω[°] 98.4

Next, an imaging lens of Example 3 will be described. The imaging lensof Example 3 has the same configurations of the lens groups as those ofthe imaging lens in Example 1. FIG. 3 is a cross-sectional viewillustrating the lens configuration of the imaging lens of Example 3.Further, regarding the imaging lens of Example 3, Table 5 shows basiclens data, Table 6 shows data regarding specs, and FIG. 9 illustratesthe aberrations.

TABLE 5 EXAMPLE 3/LENS DATA DISTANCES SURFACE RADII OF BETWEEN NUMBERSCURVATURE SURFACES nd νd  1 23.43143 3.034 1.51633 64.14  2 49.662660.100  3 16.43232 1.039 1.71299 53.87  4 6.63415 2.683  5 17.56424 0.8001.71299 53.87  6 6.12874 3.103  7 −13.47581 4.510 1.48749 70.24  8−22.84891 0.100  9 19.48408 1.086 1.80000 35.83 10 9.99724 0.791 1120.70216 4.282 1.90366 31.31 12 −28.69230 4.777 13(STOP) ∞ 2.252 14−21.36800 2.317 1.71299 53.87 15 −10.60228 0.100 16 36.49841 2.6261.61800 63.33 17 −8.50020 1.104 1.88318 24.65 18 −24.86007 0.100 1910.25621 1.675 1.89959 38.04 20 7.05702 2.853 1.49700 81.54 21 −50.722025.000 22 ∞ 0.500 1.51633 64.14 23 ∞ 2.695

TABLE 6 EXAMPLE 3/SPECS (d line) f′ 4.089 Bf′ 8.025 FNo. 1.80 2ω[°] 98.6

Next, an imaging lens of Example 4 will be described. In the imaginglens of Example 4, a front group GF constitutes of six lenses, and arear group GR consists of five lenses in which the object-side cementedlens CA, a single lens L9, and the image-side cemented lens CB aredisposed in order from the object side. FIG. 4 is a cross-sectional viewillustrating the lens configuration of the imaging lens of Example 4.Further, Table 7 shows basic lens data, Table 8 shows data regardingspecs, and FIG. 10 illustrates the aberrations.

TABLE 7 EXAMPLE 4/LENS DATA DISTANCES SURFACE RADII OF BETWEEN NUMBERSCURVATURE SURFACES nd νd  1 31.83411 2.741 1.51633 64.14  2 89.608640.100  3 17.62935 1.750 1.80518 25.42  4 5.69786 3.870  5 −25.738771.000 1.63061 59.97  6 6.89109 1.997  7 26.75278 5.010 1.73942 29.55  85.38580 4.500 1.76904 27.90  9 −16.08917 0.100 10 379.80485 1.5771.66072 32.91 11 −96.84457 3.321 12(STOP) ∞ 2.237 13 −60.48376 3.0181.48749 70.24 14 −5.95210 1.002 1.84666 23.78 15 −11.19595 0.200 1621.24954 2.409 1.71299 53.87 17 −24.76665 0.100 18 11.29793 0.8451.90366 31.31 19 6.23711 3.572 1.49700 81.54 20 ∞ 5.000 21 ∞ 0.9001.51633 64.14 22 ∞ 2.422

TABLE 8 EXAMPLE 4/SPECS (d line) f′ 4.094 Bf′ 8.016 FNo. 1.80 2ω[°] 99.8

Next, an imaging lens of Example 5 will be described. In the imaginglens of Example 5, a front group GF constitutes of five lenses, and arear group GR consists of five lenses in which the object-side cementedlens CA, a single lens L8, and the image-side cemented lens CB aredisposed in order from the object side. Note that only Example 5illustrates an example in which two optical members PP1 and PP2 arearranged. FIG. 5 is a cross-sectional view illustrating the lensconfiguration of the imaging lens of Example 5. Further, Table 9 showsbasic lens data, Table 10 shows data regarding specs, and FIG. 11illustrates the aberrations.

TABLE 9 EXAMPLE 5/LENS DATA DISTANCES SURFACE RADII OF BETWEEN NUMBERSCURVATURE SURFACES nd νd  1 41.08156 2.504 1.51633 64.14  2 149.895350.122  3 16.89654 1.820 1.80518 25.42  4 5.58217 3.206  5 −149.512510.800 1.62041 60.29  6 6.55509 4.179  7 40.75878 5.010 1.48749 70.24  89.37897 4.500 1.80610 33.27  9 −25.05255 3.179 10(STOP) ∞ 1.474 1172.98676 3.968 1.48749 70.24 12 −5.76420 0.800 1.84666 23.78 13−14.45572 0.200 14 19.07047 2.805 1.71299 53.87 15 −26.89149 0.100 1612.02229 0.872 1.90366 31.31 17 6.07890 2.796 1.49700 81.54 18 −48.386045.000 19 ∞ 0.500 1.51633 64.14 20 ∞ 0.100 21 ∞ 0.400 1.51633 64.14 22 ∞2.339

TABLE 10 EXAMPLE 5/SPECS (d line) f′ 4.096 Bf′ 8.033 FNo. 1.84 2ω[°]97.8

Next, an imaging lens of Example 6 will be described. The imaging lensof Example 6 has the same configurations of the lens groups as those ofthe imaging lens in Example 5. FIG. 6 is a cross-sectional viewillustrating the lens configuration of the imaging lens of Example 6.Further, regarding the imaging lens of Example 6, Table 11 shows basiclens data, Table 12 shows data regarding specs, and FIG. 12 illustratesthe aberrations.

TABLE 11 EXAMPLE 6/LENS DATA DISTANCES SURFACE RADII OF BETWEEN NUMBERSCURVATURE SURFACES nd νd  1 34.11452 2.837 1.51633 64.14  2 127.231000.100  3 15.81414 1.253 1.84666 23.78  4 5.60824 3.883  5 −28.522753.977 1.62280 57.05  6 7.17645 2.211  7 36.23205 3.010 1.61800 63.33  87.53791 4.294 1.80610 33.27  9 −18.38807 1.670 10(STOP) ∞ 5.423 11228.45717 3.346 1.48749 70.24 12 −6.09012 0.800 1.84666 23.78 13−13.17053 0.200 14 18.00380 2.865 1.71299 53.87 15 −25.24241 0.100 1611.27333 0.810 1.90366 31.31 17 5.88952 3.783 1.49700 81.54 18 ∞ 5.00019 ∞ 0.900 1.51633 64.14 20 ∞ 2.401

TABLE 12 EXAMPLE 6/SPECS (d line) f′ 4.121 Bf′ 7.995 FNo. 1.80 2ω[°]99.2

Table 13 shows values corresponding to conditional formulae (1) through(8) of the imaging lenses for Examples 1 through 6. Note that in all ofthe Examples, the d line is a reference wavelength, and the values shownin Table 13 below are with respect to this reference wavelength.

TABLE 13 NUMBERS OF CONDITIONAL FORMULAE FORMULAE EXAMPLE 1 EXAMPLE 2EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 (1) NnA − NpA 0.35917 0.282000.26518 0.35917 0.35917 0.35917 (2) vpA − vnA 46.46 37.71 38.68 46.4646.46 46.46 (3) NnB − NpB 0.40666 0.01036 0.40259 0.40666 0.406660.40666 (4) vpB − vnB 50.23 27.90 43.50 50.23 50.23 50.23 (5) f/fF−0.207 −0.188 −0.172 −0.054 0.029 −0.087 (6) (Rc − Rd)/(Rc + −0.464−0.124 −0.349 −1.088 0.000 0.000 Rd) (7) fA/fB 6.503 2.355 2.028 1.6554.618 1.494 (8) f/f123 −0.505 −0.598 −0.511 −0.902 −0.805 −0.957

It can be understood from the data above that all of the imaging lensesof Examples 1 through 13 satisfy conditional formulae (1) through (8)and have small F numbers with various aberrations corrected favorably.

Next, one embodiment of the imaging apparatus according to the presentinvention will be described referring to FIG. 13. FIG. 13 illustratesthe front side of a camera 10 which is a surveillance camera equippedwith an imaging lens 1 according to the embodiment of the presentinvention.

This surveillance camera 10 includes a camera body 11 equipped with alens barrel 12 housing the imaging lens 1 therewithin. The camera body11 is provided with an image sensor (not shown) in the interior thereof.This image sensor, which photographs and converts optical images formedby the imaging lens 1 into electric signals, is constituted by a CCD(Charge Coupled Device), a CMOS (Complementary Metal OxideSemiconductor), or the like, for example. Note that the image sensor isdisposed such that the optical axis Z of the imaging lens 1 intersectswith the center thereof.

The surveillance camera 10 of the present embodiment is equipped withthe imaging lens 1 of the present invention. Therefore, bright andhigh-quality images can be obtained.

Next, another embodiment of the imaging apparatus according to thepresent invention will be described referring to FIGS. 14 and 15. FIGS.14 and 15 are perspective views of the front side and the back side of acamera 30, which is a non-reflex type digital camera equipped with adetachable interchangeable lens 20 that houses an imaging lens 2according to the embodiment of the present invention within a lensbarrel.

This camera 30 includes a camera body 31 provided with a shutter button32 and a power source button 33 on the upper surface thereof. Further,operation sections 34 and 35 as well as a display section 36 are on theback surface of the camera body 31. The display section 36 displaysphotographed images and images to be photographed within the angle ofview.

A photographing aperture, into which light from a photographing objectenters, is provided in the center of the front surface of the camerabody 31, and a mount 37 is provided on a position corresponding to thephotographing aperture. Further, an interchangeable lens 20 isconfigured to be mounted to the camera body 31 through the mount 37.

The camera body 31 is provided with an image sensor (not shown), such asa CCD, and the like, which receives a subject image formed by theinterchangeable lens 20 and outputs imaging signals in response thereto;a signal processing circuit which processes imaging signals output fromthe image sensor and generates images; a recording medium for recordingthe generated images; and the like. In this camera 30, a still image ora moving image is photographed by pressing a shutter button 32 and theimage data obtained by this photography is recorded on the aboverecording medium.

The camera 30 of the present embodiment is equipped with the imaginglens 2 of the present invention. Therefore, bright and high-qualityimages can be obtained.

The present invention has been described with reference to theEmbodiments and Examples. The present invention is not limited to theembodiments and the examples described above, and various modificationsare possible. For example, values, such as the radius of curvature, thedistances between surfaces, the refractive indices, the Abbe's numbers,aspheric surface coefficients of each lens, and the like are not limitedto the values in the Examples above, but may be other values.

Further, the embodiment of the imaging apparatus were describedreferring to the drawings with a surveillance camera or a non-reflex(namely, a mirrorless) type digital camera as examples. However, theimaging apparatus of the present invention is not limited thereto, andcan be applied to various imaging apparatuses, such as industrialcameras, single-lens reflex cameras, video cameras, digital cameras,movie cameras, and broadcasting cameras.

What is claimed is:
 1. An imaging lens consisting of: in order from the object side, a front group including, in order from the most-object side, a first lens having a positive refractive power, a second lens having a negative refractive power, the second lens being of a meniscus shape with a concave surface toward the image side, and a third lens having a negative refractive power which are adjacently disposed, a stop, and a rear group consisting of two sets of cemented lenses having positive refractive powers and a single lens having a positive refractive power, the object-side cemented lens of the two sets of cemented lenses being formed by cementing, in order from the object side, a positive lens with a convex surface toward the image side and a negative meniscus lens together, and the image-side cemented lens of the two sets of cemented lenses being formed by cementing, in order from the object side, a negative meniscus lens with a concave surface toward the image side and a positive lens together, the image-side cemented lens being disposed at the most-image side in the rear group.
 2. The imaging lens as defined in claim 1, wherein the first lens is of a shape with a convex surface toward the object side.
 3. The imaging lens as defined in claim 1, wherein the front group includes a final lens, having a positive refractive power, of the front group at the most-image side.
 4. The imaging lens as defined in claim 1, wherein the following conditional formulae (1) and (2) are satisfied: 0.05<NnA−NpA<0.8  (1) 22<νpA−νnA<70  (2) where, NnA is the refractive index of the negative lens of the object-side cemented lens with respect to the d line, NpA is the refractive index of the positive lens of the object-side cemented lens with respect to the d line, νpA is the Abbe's number of the positive lens of the object-side cemented lens with respect to the d line, and νnA is the Abbe's number of the negative lens of the object-side cemented lens with respect to the d line.
 5. The imaging lens as defined in claim 1, wherein the following conditional formulae (3) and (4) are satisfied: 0<NnB−NpB<0.8  (3) 22<νpB−νnB<70  (4) where, NnB is the refractive index of the negative lens of the image-side cemented lens with respect to the d line, NpB is the refractive index of the positive lens of the image-side cemented lens with respect to the d line, νpB is the Abbe's number of the positive lens of the image-side cemented lens with respect to the d line, and νnB is the Abbe's number of the negative lens of the image-side cemented lens with respect to the d line.
 6. The imaging lens as defined in claim 1, wherein the following conditional formula (5) is satisfied: −0.5<f/fF<0.2  (5) where, f is the focal length of the entire system, and fF is the focal length of the front group.
 7. The imaging lens as defined in claim 3, wherein the following conditional formula (6) is satisfied: −10<(Rc−Rd)/(Rc+Rd)≦0  (6) where, Rc is the radius of curvature of the image-side surface of a lens adjacent to the final lens of the front group in the front group, and Rd is the radius of curvature of the object-side surface of the final lens of the front group.
 8. The imaging lens as defined in claim 1, wherein the following conditional formula (7) is satisfied: 0.1<fA/fB<10  (7) where, fA is the focal length of the object-side cemented lens, and fB is the focal length of the image-side cemented lens.
 9. The imaging lens as defined in claim 1, wherein the following conditional formula (8) is satisfied: −2<f/f123<−0.3  (8), where, f is the focal length of the entire system, and f123 is the combined focal length of the first lens through the third lens.
 10. An imaging lens consisting of: in order from the object side, a front group consisting of, in order from the most-object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a negative refractive power which are adjacently disposed, a fourth lens having a negative refractive power, and a final lens disposed at the most-image side of the front group, a stop, and a rear group consisting of two sets of cemented lenses having positive refractive powers and a single lens having a positive refractive power, the object-side cemented lens of the two sets of cemented lenses being formed by cementing, in order from the object side, a positive lens with a convex surface toward the image side and a negative meniscus lens together, and the image-side cemented lens of the two sets of cemented lenses being formed by cementing, in order from the object side, a negative meniscus lens with a concave surface toward the image side and a positive lens together, the image-side cemented lens being disposed at the most-image side in the rear group.
 11. The imaging lens as defined in claim 1, wherein the front group consists of, in order from the object side, the first lens, the second lens, the third lens, a fourth lens that is a meniscus lens with a concave surface toward the object side, a fifth lens that is a negative meniscus lens with a concave surface toward the image side, and the final lens of the front group disposed at the most-image side.
 12. The imaging lens as defined in claim 1, wherein the rear group consists of, in order from the object side, the single lens, the object-side cemented lens, and the image-side cemented lens.
 13. The imaging lens as defined in claim 1, wherein the rear group consists of, in order from the object side, the object-side cemented lens, the single lens, and the image-side cemented lens.
 14. The imaging lens as defined in claim 4, wherein at least one of the following conditional formulae (1-1) and (2-1) is satisfied: 0.25<NnA−NpA<0.6  (1-1) 25<νpA−νnA<65  (2-1) where, NnA is the refractive index of the negative lens of the object-side cemented lens with respect to the d line, NpA is the refractive index of the positive lens of the object-side cemented lens with respect to the d line, νpA is the Abbe's number of the positive lens of the object-side cemented lens with respect to the d line, and νnA is the Abbe's number of the negative lens of the object-side cemented lens with respect to the d line.
 15. The imaging lens as defined in claim 5, wherein at least one of the following conditional formulae (3-1) and/or (4-1) is satisfied: 0.25<NnB−NpB<0.6  (3-1) 25<νpB−νnB<65  (4-1) where, NnB is the refractive index of the negative lens of the image-side cemented lens with respect to the d line, NpB is the refractive index of the positive lens of the image-side cemented lens with respect to the d line, νpB is the Abbe's number of the positive lens of the image-side cemented lens with respect to the d line, and νnB is the Abbe's number of the negative lens of the image-side cemented lens with respect to the d line.
 16. The imaging lens as defined in claim 6, wherein the following conditional formula (5-1) is satisfied: −0.45<f/fF<0.1  (5-1) where, f is the focal length of the entire system, and fF is the focal length of the front group.
 17. The imaging lens as defined in claim 7, wherein the following conditional formula (6-1) is satisfied: −2<(Rc−Rd)/(Rc+Rd)≦0  (6-1) where, Rc is the radius of curvature of the image-side surface of a lens adjacent to the final lens of the front group within the front group, and Rd is the radius of curvature of the object-side surface of the final lens of the front group.
 18. The imaging lens as defined in claim 8, wherein the following conditional formula (7-1) is satisfied: 0.2<fA/fB<8  (7-1) where, fA is the focal length of the object-side cemented lens, and fB is the focal length of the image-side cemented lens.
 19. An imaging apparatus equipped with the imaging lens as defined in claim
 1. 